1. Field of the Invention
The present invention relates to a projection exposure technique for exposing a member under exposure to form a pattern of a mask (an original pattern plate) such as a photomask and a reticle thereon while the member is moved in a predetermined direction.
2. Description of the Related Art
FIG. 22 shows a projection exposure apparatus (a scan exposure apparatus) which exposes a large substrate for use in a liquid crystal display panel or the like to form a circuit pattern thereon.
In FIG. 22, reference numeral 81 shows a mask, 82 a mask scan stage, 83 a projection optical system, 84 a substrate scan stage, and 85 a substrate under exposure.
For transferring the circuit pattern to the substrate 85 in the scan exposure apparatus, exposure light is irradiated to the mask 81 which corresponds to a negative film in photography in directions indicated by small arrows in FIG. 22. The light transmitted through a mask pattern provided in the mask 81 forms an image of the mask pattern on the side of an image plane by the projection optical system 83. The substrate 85, which is disposed at the position where the mask pattern image is formed, is exposed to create the mask pattern image thereon.
In the projection exposure apparatus for exposing the large substrate for use in the liquid crystal display panel or the like to form the circuit pattern thereon, the provision of a large-diameter projection optical system capable of exposing a large substrate to form a whole desired mask pattern thereon at one time presents problems in the footprint, weight, stability, and cost of the apparatus. Thus, a certain type of projection optical system forms part of a mask pattern image in a slit-like shape, wherein a mask and a substrate are moved for scanning with respect to the projection system. This eliminates the need for the large-diameter projection optical system to allow the small apparatus to achieve exposure in a large region.
In this case, the mask 81 and the substrate 85, which are sized to take account of the size of the mask pattern image formed on the substrate 85 and the projection magnification of the projection optical system, are moved at a constant speed in directions indicated by large arrows in FIG. 22 with a controlled amount of exposure light to perform scan exposure.
A projection exposure apparatus which performs scan exposure has been proposed, for example, in Japanese Patent Application Laid-Open No. H11(1999)-219900.
In addition, Japanese Patent Application Laid-Open No. 2000-208410 has proposed a projection exposure apparatus which exposes a large substrate to form a cyclic pattern thereon through projection at a high density.
The following problems are found in the scan type exposure apparatus in which the mask stage and the substrate stage are moved when the large substrate is exposed to form the circuit pattern thereon.
(1) As the substrate is increased in size, the mask is also increased in size and the manufacturing cost of the mask is increased.
(2) A larger mask produces a warp thereof due to its own weight in the exposure apparatus to cause difficulty in providing a required exposure resolution.
(3) The entire exposure apparatus is increased in size and weight.
The problem (1) is hereinafter described in detail. In exposure of a substrate for use in a liquid crystal display panel or the like, circuit patterns for exposure include a continuous pattern having a continuous shape such as a signal line and a gate line and a discontinuous cyclic pattern consisting of mutually isolated repetitive pattern elements, for example, a gate, a source, a drain, a transparent dot electrode, and a storage capacitor electrode. It is thus difficult to employ a so-called stitching exposure method in terms of formation of the continuous pattern. As a result, the exposure apparatus generally performs exposure at a projection magnification of 1:1 to cause an increased size of the mask in association with a larger size of the substrate for a liquid crystal display panel. This presents a significant problem in time and cost involved in mask manufacture.
If the continuous pattern and the discontinuous cyclic pattern are processed in separate processes, the number of steps for exposure is increased to create disadvantages in process control and alignment, resulting in a factor which increases time and cost required for mask manufacture.
Next, the problem (2) is described in detail. The mask can be supported only at its periphery in the scan type exposure apparatus. A larger mask causes a warp thereof due to its own weight to use the margin of the focal depth of the projection system on the mask side. Thus, it is difficult to ensure a manufacture margin such as flatness on the side of the substrate, leading to difficulty in providing a required exposure resolution.